Add more explicit helpless reasons

Instead of just "while helpless", the death reason will tell
more explicitly why the player was helpless.  For example:
"while frozen by a monster's gaze"

src/polyself.c

@@ -1285,6 +1285,7 @@ dogaze()
 				    -d((int)mtmp->m_lev+1,
 					    (int)mtmp->data->mattk[0].damd)
 				    : -200);
+			    multi_reason = "frozen by a monster's gaze";
 			    nomovemsg = 0;
 			    return 1;
 			} else